Re-calibrate speedometer

I bought some Tahoe wheels off a guy the day he brought his truck home. The tires on these wheels are 265/17 & what came on my truck was 245/17. Now, my GPS says I'm actually running 2mph or so over what the speedometer says. How do I go about getting the speedometer to account for the "extra" tire?

if its only 2 mph over i personally wouldn't worry about it. after i went from 265 to 315's mine was 5 mph difference between the gps and speedo

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I have thought about just not worrying with it, but , if the dealer can do it & not charge me, I guess I'll go through with it, but until I have enough $ for a tuner, I'll just watch the gps. Little things like this tend to bug me until eventually I get it fixed.

I'm unclear about these tuners. Do they just reprogram the cpu on the truck & you unplug it, or is it something that's got to sit on the dash (or where ever) & stay there? I guess what I'm saying is I wonder if I could get a shop to reprogram the cpu instead of buying the programmer? Do they have these used?

some tuners will have to stay connected, but most wont. I highly recommend waiting and getting a DiabloSport Predator when you can afford it. I was skeptical about how much a tuner could do for a gas engine truck, but the Predator made a night-and-day difference. You just plug it in, program the things you want to change, including your gear ratio if you were ever to do a gear swap, and your tire size, among many others. When you are done, you just unplug it. If you need to take the truck in for warranty work, you just tell it to restore the factory tune (it saves it before it changes anything), and there is no trace of it having been there.

I know I'm about 4 years late to the party, but in case someone comes across this like I did, I wanted to share couple things about the recalibrator and tuners. The hypertech speedometer calibrator linked above does not allow you to adjust for gear changes, although it's since been replaced by one that does not have that note, not sure if the new ones do. It may not be an issue for you now, but in my case I blew up my rear axle and replaced it with one that had a different gear ratio. My DiabloSport Predator tuner allowed me to adjust for that, once I got it 'flashed' with the latest firmware. I got one of the first versions that only allowed custom programs if you ran premium gas. With the upgrade it has 87 octane tunes. Between going from 3.83 to 3.42 gears and the stock 16" tires to much larger, newer 17" from a Yukon, my speedo was off 15mph at highway speeds. And although it's not as fast off the line, my gas mileage increased dramatically. I'm not sure about the Hypertech programmers, but with the DiabloSport you upload the program and then unplug it- at that point, the programmer is 'locked' to that vehicle until you restore the stock program to the truck. So you can't borrow one or buy one and use it on multiple vehicles. Before the new firmware upgrade, once you used it on a vehicle, it was permanently locked to that vehicle even if you restored, so you couldn't keep it to use with another vehicle if you got rid of your current one. Thankfully they changed that. Also I can now do free firmware upgrades by downloading them instead of sending it back and paying $100. So while you can now get used ones that will work as long as the previous owner restored his original program, it's probably better to just buy a new one so you don't have to worry about that or whether it has the old firmware.

I'm looking for a way to recalibrate my speedo so I can keep my tuner and sell the truck, as I plan on replacing it with a compatible vehicle. Don't really want to spend $200+ though, especially since Summit has new Predator tuners for $199 now.